US EPA

2585733 

Journal Article 

Nanostructured thin layers of vanadium oxides doped with cobalt, prepared by pulsed laser ablation: structure, chemistry, morphology, and magnetism 

Teodorescu, CM; Socol, G; Negrila, C; Luca, D; Macovei, D 

2008 

435-438 

WOS:000272169500114 

Cobalt-doped vanadium oxide thin layers prepared by pulsed laser ablation are investigated by (i) X-ray photoelectron spectroscopy, (ii) the local atomic order by X-ray absorption near-edge structure (XANES), (iii) the morphology of the films was investigated by atomic force microscopy (AFM), and (iv) magnetic properties were quantified by magneto-optical Kerr effect (MOKE). In most cases, the chemical composition of the host matrix was found to be the vanadium (5+) oxide V(2)O(5) at the sample surface and lower ionization states (+2 and +3) in the bulk. Co ions are found either in high ionization state Co(5+) (for samples synthesized in high vacuum condition, denoted by VO1), or with Co in lower ionization states Co(4+) (for samples synthesized in a mixture of argon and oxygen atmosphere, denoted by VO2). Consistent information was obtained from chemical shifts from individual core level scans in XPS, compared with existent data in litterature, and the amplitude of the pre-edge peak in XANES, which is a sign of quadrupole 1s -> 3d dipole-forbidden transition and whose amplitude is proportional to the number of 3d vacancies per atom. AFM revealed big particles with sizes > 100 mu m for VO1 samples, whereas smaller nanoparticles with sizes ranging between 20 and 30 mu m were observed for VO2 samples. VO1 samples presented very high coercitive fields with a relatively low saturation magnetisation at room temperature, whereas VO2 samples presented double-loop hysteresis curves, indicating the coexistence of exchange bias between two kinds of magnetic moieties with strong anisotropy. 

vanadium oxide; pulsed laser deposition; XPS; XAFS; magnetic properties